1. Field
The presently disclosed subject matter relates to a method for manufacturing an optical deflector which can be applied to a projection-type display system, for example.
2. Description of the Related Art
Recently, in a projection-type display system, a spotlight from a light source is deflected by an optical deflector and then, is projected onto a screen. The optical deflector includes a two-dimensional optical deflector chip which is a micro electro mechanical system (MEMS) device manufactured by using semiconductor manufacturing processes and micro machine technology, and a package for protecting the two-dimensional optical deflector chip.
Generally, the two-dimensional optical deflector includes a mirror for reflecting a spotlight from a light source, a movable frame surrounding the mirror for supporting the mirror, an inner actuator for vibrating (rocking) the mirror with respect to an X-axis of the mirror, a support body surrounding the movable frame, and an outer actuator for rocking the mirror through the movable frame with respect to a Y-axis of the mirror perpendicular to the X-axis.
As a first example, the inner actuator is constructed by torsion-bar type piezoelectric actuators for rocking the mirror through torsion bars, and the outer actuator is constructed by other torsion-bar type piezoelectric actuators for rocking the movable frame through other torsion bars (see: JP2008-20701A). Also, as a second example, the inner actuator is constructed by torsion-bar type piezoelectric actuators for rocking the mirror through torsion bars, and the outer actuator is constructed by meander type piezoelectric actuators for rocking the movable frame (see: JP2009-223165A). Further, as a third example, the inner actuator is constructed by meander type piezoelectric actuators for rocking the mirror, and the outer actuator is constructed by other meander type piezoelectric actuators for rocking the movable frame (see: JP2010-122480A and US2011/0292479A1).
The optical deflector has an advantage in that the structure is small and simple and the drive power is not so large. In order to effectively exhibit this advantage, the package is preferably as small as possible.
In a first prior art method for manufacturing an optical deflector, an optical deflector chip is die-bonded by using resin to a ceramic package, and then, a wire-bonding operation is performed between electrode pads of the optical deflector chip and electrode pads of the ceramic package.
In the above-described first prior art method, however, since spacing for bonding wires is required in the ceramic package, the ceramic package would be larger in size than the optical deflector chip. Also, since the ceramic package is sintered, the size in step and the width in periphery of the ceramic package cannot be reduced. Thus, the entire optical deflector would be large in size. Note that, if the optical deflector chip per se is reduced in size, it may be possible to reduce the entire optical deflector. In this case, however, the optical deflector chip needs to be redesigned to increase the developing period.
In a second prior art method for manufacturing an optical deflector, a wireless wafer-level package technology is adopted (see: JP2005-19966A). That is, a silicon wafer on which a plurality of MEMS chips corresponding to optical deflector chips are arranged is adhered to a cap wafer on which sealing caps are arranged. Then, through silicon vias (TSVs) are formed within the silicon wafer to electrically connect the MEMS chips to electrodes on the external surface of the silicon wafer. Finally, the silicon wafer and the cap wafer are diced along scribing lines thereof by using dicing blades or the like to separate one of the MEMS chips associated with one of the sealing caps from each other. Thus, the size of each of the diced sealing caps is the same as that of the diced MEMS chips, so that the entire optical deflector would be reduced in size.
In the above-described second prior art method, however, since the TSVs need to be formed within the silicon wafer, the manufacturing yield would be reduced, so that the manufacturing cost would be increased.
Also, even if the silicon wafer includes defective MEMS chips, such defective MEMS chips would be assembled by sealing caps, which also would increase the manufacturing cost.
Further, when the silicon wafer is diced by a dicing process using dicing blades, very small defects, i.e., so-called tipping would be generated in the MEMS chips of the silicon wafer, so that the manufacturing yield would be reduced, which further would increase the manufacturing cost.